There is a conventional omnidirectional imaging system that performs full-circumference imaging through the use of two reflections between a plurality of rotator mirrors whose rotation axes coincide with each other (for example, see Patent Literature (PTL) 1). FIG. 29 shows a conventional omnidirectional imaging system described in PTL 1.
In FIG. 29, a primary mirror 301 reflects light incident in directions of horizontal 360 degrees of surroundings. A secondary mirror 302 further reflects the light reflected by the primary mirror 301. The light reflected by the secondary mirror 302 passes through a principal point of a photoreceiving lens system 303, and forms an image on an image plane 304. Note that the primary mirror 301 and the secondary mirror 302 are covered with a transparent tube 305. Thus, the optical system in FIG. 29 can image a subject in directions of horizontal 360 degrees of surroundings, by one photoreceiving lens system.
As another example, there is an omnidirectional imaging system that obtains distance information using a plurality of mirrors (for example, see PTL 2). FIG. 30 shows a conventional omnidirectional imaging system described in PTL 2.
In FIG. 30, an omnidirectional mirror 401 includes a hemispherical mirror 402a and a plurality of spherical mirrors 402b. The hemispherical mirror 402a reflects light incident in directions of horizontal 360 degrees of surroundings, and the plurality of spherical mirrors 402b also reflect light incident in directions of horizontal 360 degrees of surroundings. The light reflected by the hemispherical mirror 402a and the plurality of spherical mirrors 402b is imaged by an imaging device 403. Thus, the optical system in FIG. 30 can capture an image of one subject reflected by the hemispherical mirror and the plurality of spherical mirrors and measure a distance to the subject based on the image.
As another example, there is an omnidirectional imaging system that obtains distance information using a fisheye lens and a rotator mirror (for example, see PTL 3). FIG. 31 shows a conventional omnidirectional imaging system described in PTL 3.
In FIG. 31, a camera 510 includes a fisheye lens al and a rotator mirror δ. The camera 510 has a section that directly forms an image in a part of an imaging device 514 through the fisheye lens al and a lens optical system 512, and a section that forms an image in a part of the imaging device 514 through the fisheye lens al and the lens optical system 512 after reflection by the rotator mirror δ. The omnidirectional imaging system in FIG. 31 obtains distance information to a subject, from the section that directly forms an image through the fisheye lens α1 and the section that forms an image through the fisheye lens α1 after reflection by the rotator mirror δ.